BACTERIAL GENETICS (LECTURE 11)

Question 1

What are the 2 components that make up the bacterial genome?

Answer 1

There is the bacterial chromosome and the plasmid (non-chromosomal DNA).

Question 2

Describe the structure of the bacterial chromosome. Where is it located and what genes does it contain?

Answer 2

Double stranded, circular DNA molecule. Found in nucleoid region. Contains essential genes for survival.

Question 3

Describe the structure of the plasmid (non-chromosomal DNA).

Answer 3

Small, circular, double stranded DNA molecule.

Question 4

What genes are found in plasmids?

Answer 4

Genes that are not required for survival but that can give bacteria an advantage under changing environmental conditions (such as antibiotic resistance).

Question 5

What is an episome?

Answer 5

It is a segment of DNA that can exist as a plasmid or be integrated into the bacterial chromosome.

Question 6

How do bacteria replicate?

Answer 6

Bacteria replicate by binary fission.

Question 7

Since bacteria replicate by binary fission, what can be said about origins of replication on bacterial chromosomes?

Answer 7

Each chromosome has a single origin of replication.

Question 8

Do plasmids also replicate during binary fission?

Answer 8

Yes.

Question 9

What is a possible outcome of genetic recombination in bacteria?

Answer 9

Genetic recombination can produce new bacterial strains.

Question 10

What is genetic recombination?

Answer 10

Combining DNA from two different sources.

Question 11

What are the 3 methods of genetic recombination in bacteria? What is the source of external DNA for each?

Answer 11

(1) Transformation (environment), (2) Transduction (bacteriophages) and (3) Conjugation (between bacteria).

Question 12

Describe bacterial transformation.

Answer 12

Bacterial cells take up foreign DNA from environment (such as a plasmid) and this foreign DNA can remain as a plasmid or be incorporated into the bacterial chromosome by recombination.

Question 13

Provide an example of bacterial transformation.

Answer 13

Harmless R-cells become transformed to a pathogenic stain when they take up DNA from S-cells.

Question 14

What is transduction? What does it result in?

Answer 14

Transduction is when genes are transferred form one bacteria to another by a bacteriophage. It results in the random transfer of genes!

Question 15

Does transduction occur during the lytic or lysogenic life cycle?

Answer 15

Lytic life cycle.

Question 16

Describe the journey of foreign DNA during transduction.

Answer 16

Pieces of host 1’s DNA are packaged into new bacteriophages during viral assembly. When bacteriophage infects new host, it inserts DNA from the previous host. Recombination occurs between the introduced DNA and the bacterial chromosome.

Question 17

What is conjugation?

Answer 17

It is the direct transfer of genes between 2 bacterial cells.

Question 18

Name a bacteria that can perform conjugation.

Answer 18

E. Coli

Question 19

Describe the steps involved in conjugation.

Answer 19

Donor cell extends an external appendage called the sex pilus. Sex pilus attaches to recipient cell and a cytoplasmic bridge is formed between the 2 cells. DNA can be transferred across the bridge.

Question 20

What is the F factor?

Answer 20

The ability to form sex pili and to transfer DNA is conferred by a special piece of DNA called the F factor.

Question 21

What does F factor abbreviate?

Answer 21

Fertility factor.

Question 22

Is a donor F+ or F-?

Answer 22

A donor has the fertility factor, it is F+.

Question 23

Is a recipient F+ or F-?

Answer 23

A recipient does not have the fertility factor, it is F-.

Question 24

Describe F+ cells. (3)

Answer 24

These contain the F factor, F factor is passed onto offspring and it can donate the F factor.

Question 25

Describe F- cells.

Answer 25

These lack the F factor but can receive the F factor.

Question 26

Is the F factor in the plasmid or chromosome?

Answer 26

It can be in either one.

Question 27

Describe conjugation where the F factor is in the plasmid. (3)

Answer 27

The sex pilus forms a cytoplasmic bridge between donor (F+) and recipient (F-) cell. F plasmid replicates and is transferred to F- cell. F- cell becomes F+ cell.

Question 28

What name is given to F+ cells where the F factor is in the chromosome?

Answer 28

Cells with F factor in chromosome are called high frequency of recombination cells - Hfr cells.

Question 29

Is a recipient cell guaranteed to become F+ when receiving from an Hfr cell?

Answer 29

No, the recipient cell will often not become F+.

Question 30

Describe conjugation where the F factor is in the chromosome. (5)

Answer 30

Hfr cell forms bridge with F- cell and transfers the F factor. Some of the bacterial chromosome surrounding the F factor is also transferred. Amount of Hfr DNA transferred is random and depends on when the connection is broken (therefore the recipient will not always become F+). Recombination will occur creating a new bacterial chromosome.

Question 31

Why are Hfr cells very efficient at creating recombinant bacteria?

Answer 31

Because bacterial genes are delivered along with the F factor during conjugation.